Structures for testing circuits and methods for fabricating the structures

ABSTRACT

One embodiment of the present invention is a structure useful for testing circuits that includes: (a) a substrate having contactors on a first side and pads on a second side; (b) a card having pads on a first side; and (c) interconnectors that electrically connect the pads on the second side of the substrate with the pads on the card; wherein at least one of the interconnectors includes at least a portion that does not melt at temperatures in a range from about 183° C. to about 230° C., and the distance between the substrate and the card is determined by a dimension of the at least a portion.

[0001] This is a continuation-in-part of a patent application entitled“Structures for Testing Circuits and Methods for Fabricating theStructures” having Ser. No. 10/387,216 which was filed on Mar. 12, 2003.This application is also related to a patent application entitled“Structures for Testing Circuits and Methods for Fabricating theStructures” having Ser. No. 10/386,875 which was filed on Mar. 12, 2003.

TECHNICAL FIELD OF THE INVENTION

[0002] One or more embodiments of the present invention pertain to: (a)one or more structures useful, for example and without limitation, fortesting circuits, for example and without limitation, integratedcircuits (“ICs”) at a wafer level; and (b) one or more methods forfabricating such structures.

BACKGROUND OF THE INVENTION

[0003] As is known, a substrate (sometimes also referred to in the artas an interposer) is a device that provides a fan-out between I/O (i.e.,electrical inputs and outs) of a circuit, for example and withoutlimitation, an integrated circuit (“IC”) and a Probe Card to enabletesting of the IC, for example, at a wafer level. Such a substrate maybe a rigid substrate, a semi-flex substrate, a flex substrate, and soforth, and such substrates often have a relatively low cost whencompared to that of the Probe Card.

[0004] As IC geometries have decreased in size dramatically since suchdevices were first introduced several decades ago, so too havegeometries associated with wiring connections to their I/O. For example,present designs include the use of bumped wafer pad pitches of 200 μm orless. In order to test such ICs, one is required to utilize high densityinterconnect (“HDI”) substrates having matching fine connector pitches.

[0005] Substrates available today, and the manner in which they areused, are problematic for two basic reasons. First, manufacturingtechniques used to fabricate such substrates and to connect them toProbe Cards typically require multiple expensive steps. Second, if oneof the connectors on the substrate gets damaged, it cannot be replaced,for the most part, or is difficult or expensive to rework. In addition,whenever the substrate wears out, or gets damaged, one typically has tothrow away the Probe Card together with the substrate. In particular,this is because, due to manufacturing techniques used to fabricate suchsubstrates and to connect them to Probe Cards, it is a prohibitivelylengthy and costly process to separate the substrate from the ProbeCard.

[0006] In light of the above, there is a need in the art for: (a) one ormore structures useful, for example and without limitation, for testingcircuits, for example and without limitation, ICs at a wafer level thatsolve one or more of the above-identified problems; and (b) one or moremethods for fabricating such structures.

SUMMARY OF THE INVENTION

[0007] One or more embodiments of the present invention satisfy one ormore of the above-identified needs in the art. In particular, oneembodiment of the present invention is a structure useful for testingcircuits that comprises: (a) a substrate having contactors on a firstside and pads on a second side; (b) a card having pads on a first side;and (c) interconnectors that electrically connect the pads on the secondside of the substrate with the pads on the card; wherein at least one ofthe interconnectors includes at least a portion that does not melt attemperatures in a range from about 183° C. to about 230° C., and thedistance between the substrate and the card is determined by a dimensionof the at least a portion.

BRIEF DESCRIPTION OF THE DRAWING

[0008]FIG. 1 is a cross sectional view that shows a pinalignment fixtureused to connect a substrate to a Probe Card in accordance with one ormore embodiments of the present invention prior to re-flow;

[0009]FIG. 1A is a cross sectional view that shows a stiffeningmechanism connected to a Probe Card in accordance with one or moreembodiments of the present invention;

[0010]FIG. 1B is a bottom view that shows the stiffening mechanism shownin FIG. 1A;

[0011]FIG. 2 is a top view that shows a portion of a flex substrate thatis fabricated in accordance with one or more embodiments of the presentinvention;

[0012]FIGS. 3-5 are cross sectional views that show substrates whichhave bevels formed on the edges of the substrates that have beenfabricated in accordance with one or more embodiments of the presentinvention;

[0013]FIG. 6 shows a clamp mechanism that is fabricated in accordancewith one or more embodiments of the present invention;

[0014]FIG. 7 is a cross sectional view that shows a chip substrate thatis fabricated in accordance with one or more embodiments of the presentinvention;

[0015]FIG. 8 shows a Pogo pin used to fabricate one or more embodimentsof the present invention;

[0016]FIG. 9 is a top perspective view that shows a connector-holderbottom plate that is fabricated in accordance with one or moreembodiments of the present invention;

[0017]FIG. 10 is a bottom perspective view that shows a connector-holdertop plate that is fabricated in accordance with one or more embodimentsof the present invention;

[0018]FIG. 11 is a cross sectional view that shows a hole in theconnector-holder bottom plate shown in FIG. 9;

[0019]FIG. 12 is a cross sectional view that shows a hole in theconnector-holder top plate shown in FIG. 10;

[0020]FIG. 13 is an exploded view that shows a portion of a structureused to test circuits that is fabricated in accordance with one or moreembodiments of the present invention;

[0021]FIG. 14 is a cross sectional view that shows a groove cut into aside of a substrate that is fabricated in accordance with one or moreembodiments of the present invention;

[0022]FIG. 15 is a top view of a clamp that is fabricated in accordancewith one or more embodiments of the present invention;

[0023]FIG. 16 is a cross sectional view that shows a structure fortesting circuits that is fabricated in accordance with one or moreembodiments of the present invention;

[0024]FIG. 17 is a top view that shows a substrate and an RF interfaceboard that are used in the structure shown in FIG. 16; and

[0025]FIG. 18 is a cross sectional view of a structure that isfabricated in accordance with one or more embodiments of the presentinvention.

DETAILED DESCRIPTION

[0026] As is known, circuits such as, for example and withoutlimitation, integrated circuits (“ICs”), are fabricated on wafers, andthe circuits are tested by applying electrical signals to circuit inputsand analyzing electrical signals produced at circuit outputs (suchcircuit inputs and outputs may be bumped or not). As is also known, aProbe Card that provides an interface between the circuit inputs andoutputs (“I/O”) on the wafer and a Tester is used to perform suchtesting.

[0027] As the density of I/O of ICs has increased, it has become commonto connect the Probe Card to a substrate (sometimes referred to in theart as an interposer) having an array of contactors (for example andwithout limitation, 12-50 μm high structures that are sometimes alsoreferred to in the art as posts) on a top or testing side (i.e., a sidethat contacts the IC on the wafer) and having a ball grid array (“BGA”)of pads on a bottom side (i.e., a side that contacts the Probe Card).The contactors are wired through the substrate, and each wire ends at apad in the BGA on the bottom side of the substrate. The array ofcontactors has a pitch and density (sometimes referred to as afootprint) that matches that of the IC, and the BGA has a pitch anddensity that matches that of the Probe Card. Substrates used to testpresent and future ICs, may be high density interconnect (“HDI”)substrates where the pitch of the array of contactors could be as smallas 125 μm or less. Thus, one or more embodiments of the presentinvention relate to methods for assembling a structure used to testcircuits, for example and without limitation, ICs, whether bumped orriot, on a wafer, and one or more further embodiments relate to theassembled structure itself.

[0028] In particular, one or more embodiments of the present inventionare methods for connecting a substrate, for example and withoutlimitation, a rigid substrate, a flex substrate, a semi-flex substrate,a silicon/glass substrate (for example and without limitation, asilicon/glass structure that includes MEMS-type spring contactors), andso forth, to a Probe Card to provide structures that are used, forexample and without limitation, to test circuits, for example andwithout limitation, integrated circuits (“ICs”), whether bumped or not,on a wafer. Advantageously, in accordance with one or more embodimentsof the present invention, structures are produced that may be used costeffectively for testing because, among other reasons, such substratesmay be replaced easily and rapidly with a new ones whenever thesubstrates are damaged or worn. In addition, advantageously, inaccordance with one or more embodiments of the present invention,structures are produced having a relatively short distance between thesubstrate and the Probe Card, whereby electrical connections between thesubstrate and the Probe Card have better electrical properties thanthose of structures produced using prior art methods.

[0029] The following describes a method (“Method I”) for connecting asubstrate to a Probe Card (i.e., for connecting BGA pads of a substrateto BGA pads of a Probe Card) in accordance with one or more embodimentsof the present invention, which substrate can be, for example andwithout limitation, a rigid substrate, a flex substrate, or a semi-flexsubstrate. FIG. 1 is a cross sectional view that shows a pinalignmentfixture used to carry out Method I prior to re-flow.

[0030] As shown in FIG. 1, the pinalignment fixture includes base plate100. Base plate 100 is, for example and without limitation, an aluminumbase plate, a Durostone® composite material base plate, or a base platethat is fabricated using any one of a number of other materials that arewell known to those of ordinary skill in the art, which materials arerelatively stable at processing temperatures of subsequent steps ofMethod I. In accordance with one or more embodiments of the presentinvention, base plate 100 has an area of about the same size as that ofProbe Card 130, and base plate 100 has a thickness in a range, forexample and without limitation, from about 5.0 mm to about 7.0 mm. Asfurther shown in FIG. 1, the pinalignment fixture includes alignmentpins that are affixed to base plate 110 such as alignment pins 120 and121. In accordance with one or more embodiments of the presentinvention, the alignment pins have a diameter in a range, for exampleand without limitation, from about 0.7 mm to about 1.1 mm diameter. Asone can readily appreciate, the pinalignment fixture may include, forexample and without limitation, three (3) or four (4) such alignmentpins.

[0031] In a first, optional step of Method I, release film 110 such as,for example and without limitation, a Mylar film or a Teflon film, isaligned with, and placed over, base plate 100 of the pinalignmentfixture (holes in release film 110 match the positions of the alignmentpins such as pins 120 and 121). Next, Probe Card 130 is aligned with,and placed over, release film 110 on the pinalignment fixture (holes inProbe Card 130 match the positions of the alignment pins such as pins120 and 121). Vias 141 and 142 are formed in a commercially available“interconnector alignment” film such as, for example and withoutlimitation, polyimide film 150 having adhesive (not shown) (for exampleand without limitation, epoxy, acrylic, epoxy-acrylic, and so forth) onone, or both, side(s), and a release film (not shown) (for example andwithout limitation, a Mylar film or Teflon film) disposed on theadhesive side. Vias 141 and 142 may be formed in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art such as, for example and without limitation, by drilling,punching, lasing, and so forth. The locations of vias 141 and 142 inpolyimide film 150 match the locations of BGA pads 131 and 132,respectively, on the top side of Probe Card 130. Although not shown assuch in FIG. 1, the cross sectional area of vias 141 and 142 istypically larger that the cross sectional areas of pads 131 and 132,respectively. As one can readily appreciate, the step of fabricating theinterconnector alignment film (i.e., polyimide film 150) may take placeat any time before it is needed to be placed in use. Next, polyimidefilm 150 is aligned with, and placed over, Probe Card 130 on thepinalignment fixture (holes in polyimide film 150 match the positions ofthe alignment pins such as pins 120 and 121). Next, weight 210, forexample, an aluminum or stainless steel plate having a thickness in arange, for example and without limitation, from about 10 mm to about12.7 mm, and having an area of about the same size as that of Probe Card130 is aligned with, and placed over polyimide film 150 on thepinalignment fixture to apply pressure to polyimide film 150 (holes inplate 210 match the positions of the alignment pins such as pins 120 and121). Next, polyimide film 150 is laminated to Probe Card 130 by, forexample and without limitation, baking in an oven. The oven temperatureis in a range, for example and without limitation, from about 150° C. toabout 200° C., the pressure exerted by the weight of plate 210 is in arange, for example and without limitation, from about 14 kg/cm² to about28 kg/cm², and the time spent in the oven is in a range, for example andwithout limitation, from about 1 hour to about 2 hours. Next, weight 210is removed.

[0032] Next, vias 141 and 142 are filled with paste 171 and 172,respectively, using, for example and without limitation, the releasefilm of polyimide film 150 as a mask. Paste 171 and 172 may be any oneof a number of conductive pastes that are well known to those ofordinary skill in the art such as, for example, and without limitation,a Ag conductive paste, a Au conductive paste, a Cu conductive paste, andso forth, or it may be any one of a number of solder pastes that arewell known to those of ordinary skill in the art. Paste 171 and 172 maybe applied utilizing any one of a number of methods that are well knownto those of ordinary skill in the art such as, for example and withoutlimitation, methods utilizing a dispensing machine, methods utilizingscreen-printing, methods utilizing a squeegee, and so forth. Also, inaccordance with one or more further embodiments of the presentinvention, paste 171 and 172 can be a compliant, conductive paste. Sucha compliant conductive paste may be any one of a number of such productsthat are well known to those of ordinary skill in the art such as, forexample and without limitation, an elastomer such as a siliconeelastomer having conductive particles embedded therein. The use of acompliant conductive paste may be advantageous in that the resultingstructure (sometimes referred to as a “lay-up”) may be able to take upvertical movements or movements in a Z-direction caused during testingby non-planarity of contactors on the substrate, pads on the substrate,pads on the Probe Card, and/or I/O contacts on the wafer. Next, therelease film is removed.

[0033] Next, a stencil (sometimes referred to in the art as a solderball stencil—not shown) that is fabricated in accordance with any one ofa number of methods that are well known to those of ordinary skill inthe art is aligned with, and placed, over polyimide film 150 on thepinalignment fixture (holes in the stencil match the positions of thealignment pins such as pins 120 and 121); the edges of the stencil couldhave a corral formed thereon, for example, a corral of tape, to trapballs within the confines of the stencil. The holes in the stencil areslightly larger than the largest cross section of interconnectors, forexample and without limitation, balls (described below), so theinterconnectors, for example and without limitation, balls, will fallthrough the holes in the stencil when the stencil is removed. Inaccordance with one or more embodiments of the present invention, balls181 and 182 shown in FIG. 1 are comprised of a rigid core, for exampleand without limitation, a solid copper (Cu) core, and a coating, forexample and without limitation, a solder coating such as, for exampleand without limitation, a eutectic solder coating. Next, balls 181 and182 are placed over the stencil, and the stencil is removed. Thediameter of the core of balls 181 and 182 is in a range, for example andwithout limitation, from about 5 mils to about 10 mils, and the coatinghas a thickness in a range, for example and without limitation, fromabout 20 μm to about 25 μm. The diameter of the core of balls 181 and182 ought to be larger than the thickness of polyimide film 150 so thatthe core of balls 181 and 182 can contact pads 191 and 192,respectively, on substrate 190 and pads 131 and 132, respectively, onProbe Card 130.

[0034] Next, substrate 190 (for example and without limitation, a rigidsubstrate, a flex substrate, a semi-flex substrate, and so forth) isaligned with, and placed over balls 181 and 182 on the pinalignmentfixture (holes in substrate 190 match the positions of the alignmentpins such as pins 120 and 121). Next, optional release film 200, forexample and without limitation, a Mylar or Teflon film, is aligned with,and placed over, structure 190 (and contactors 195 and 196) on thepinalignment fixture 1000 (holes in release film 200 match the positionsof the alignment pins such as pins 120 and 121, for example and withoutlimitation, release film 200 may have a cut-out region where the cut-outregion includes an area in which the contactors are disposed so thatthey are not damaged during re-flow). Next, weight 210 is aligned with,and placed over, release film 200 on the pinalignment fixture 1000 toapply pressure. Next, the solder coating on balls 181 and 182 isre-flowed, for example and without limitation, by baking in an oven at atemperature in a range, for example and without limitation, from about200° C. to about 230° C. Advantageously, polyimide film 150 holds balls181 and 182 in place during the re-flow, and it helps support each ballduring testing. During the re-flow process, weight 210 provides a forcethat causes the solder to flow so that the distance between substrate190 and Probe Card 130 is determined by a dimension of the core of balls181 and 182, for example and without limitation, the diameter of a Cucore of balls 181 and 182 (it should be understood that other mechanismsfor applying such a force may be used to fabricate one or more furtherembodiments of the present invention such as, for example and withoutlimitation, by the use of springs that are adapted to urge substrate 190and Probe Card 130 towards each other). Thus, the rigid core of balls181 and 182 acts as a stopper to vertical displacement of substrate 190relative to Probe Card 130. Since three (3) points determined a plane,the plane of substrate 190 will be determined substantially by thediameter of the three largest cores (where the core diameters areexpected to vary due to manufacturing tolerances). Advantageously,Method I provides a structure wherein a plane of substrate 190 issubstantially parallel to a plane of Probe Card 130. Finally, thestructure or lay-up comprised of connected substrate 190 and Probe Card130 is removed from the pinalignment fixture, and release films 110 and200 are removed.

[0035] In accordance with one or more further embodiments of the presentinvention, a stiffening mechanism is connected to a side of the ProbeCard opposite from the side to which the substrate is connected. FIG. 1Ais a cross sectional view that shows how stiffening mechanism 447 isconnected to Probe Card 457 in accordance with one or more embodimentsof the present invention, and FIG. 1B is a bottom view that showsstiffening mechanism 447. As shown in FIG. 1A, stiffening mechanism 447is connected to Probe Card 457 so that substrate 467 is encompassedwithin an area delineated by the perimeter of stiffening mechanism 447.As further shown in FIG. 1A, the area delineated by the perimeter ofstiffening mechanism 447 does not include electrical contacts 477disposed on Probe Card 457, which electrical contacts 477 provideelectrical connections between Probe Card 457 and a test interfacesystem.

[0036] As shown in FIG. 1A, stiffening mechanism 447 includes legstructure 451 that is used to connect ring structure 448 (shown in FIG.1B) to Probe Card 457 at a multiplicity of locations about the peripheryof stiffening mechanism 447. Leg structure 451 may comprise, for exampleand without limitation, a number of legs, leg structure 451 may be aring, and so forth. Stiffening mechanism 447 is connected to Probe Card557 using a connection mechanism such as, for example and withoutlimitation, screws and nuts. Also, in accordance with one or morealternative such embodiments, ring structure 448 shown in FIG. 1B mayfurther include supports such as radial arms, struts, ribs, and thelike. In accordance with one or more further embodiments of the presentinvention, stiffening mechanism 447 may be comprised of a solid plate,with or without a leg structure like leg structure 451 described above.Lastly, stiffening mechanism 447 may be fabricated from any one of anumber of materials such as, for example and without limitation, as ametal, a plastic, a ceramic, and so forth. Advantageously, in accordancewith such embodiments of the present invention, stiffening mechanism 447provides support for substrate 467 during testing.

[0037] It should be understood by those of ordinary skill in the artthat balls 181 and 182 utilized in the above-described embodiment of thepresent invention are interconnectors that provide electrical continuitybetween pads on the bottom or non-testing side of the substrate and padson the top side of the Probe Card. In general, the interconnectors maybe any type of electrical conductor (for example and without limitation,it is comprised of an electrical conducting material): (a) whoseelectrical conductivity is sufficient to satisfy design electricalrequirements of a resulting structure or lay-up; and (b) that has atleast a core that does not melt as a result of applying heat during thefabrication process. For example and without limitation, the core doesnot melt at temperatures used to re-flow eutectic solder (for example,temperatures in a range from about 183° C. (the melting point ofeutectic solder) to about 230° C.). Thus, for this case, for example,and without limitation, the core may be a material that melts at atemperature that is higher than 230° C. since such a material would notmelt in the specified range. In light of this, when the interconnectorsare embodied as balls, such balls may be: (a) solid Cu balls; (b) solidCu balls that are coated with eutectic solder; (c) solid Indium alloyballs; (d) solid Indium alloy balls that are coated with solder; (e)solid high lead solder (for example and without limitation, 97/3 or95/5) balls; (f) solid high lead solder (for example and withoutlimitation, 97/3 or 95/5) balls that are coated with solder; and (g) soforth. In addition, further embodiments can be fabricated wherein thecore of the interconnectors (for example and without limitation, balls)is not solid, and further embodiments can be fabricated wherein the coreof the interconnectors (for example and without limitation, balls)comprises a ceramic material that is embedded with a conducting materialsuch as, for example, and without limitation, gold, Cu, silver, Indium,Ni, and so forth. Embodiment of such balls may be fabricated inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art, and one or more embodiments of suchballs are commercially available.

[0038] In accordance with one or more further embodiments of the presentinvention, the interconnectors may be compliant conductive balls, forexample and without limitation, compliant conductive plastic balls. Forexample, suitable conductive, compliant balls are commercially availablethat have a plastic core (for example and without limitation, a plasticcore having a hollow center), which plastic core is surrounded or coatedwith: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) alayer of Cu, a layer of Ni, and a layer of Au; (d) one or more of alayer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. Inaddition, in accordance with one or more still further embodiments ofthe present invention, the interconnectors may be springs (suitablesprings may be obtained commercially). Advantageously, in accordancewith one or more such embodiments of the present invention, suchcompliant, conductive balls may compress when the structure is used in aTester and, thereby, the compliant, conductive balls may be able make upfor any non-planarity of the structure as a whole.

[0039] It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to thesubstrate and to the Probe Card utilizing any one of a number of methodsthat are well known to those of ordinary skill in the art. For exampleand without limitation, if an interconnector is embodied as a soldercoated Cu ball, such a solder coated ball may be affixed: (a) byre-flow; (b) by re-flow after applying flux to the substrate and/or theProbe Card; (c) by re-flow after applying conductive paste to thesubstrate and/or the Probe Card; (d) by re-flow after applyingconductive paste to the substrate or the Probe Card and applying flux tothe Probe Card or the substrate, respectively; (e) and so forth. As afurther example, if an interconnector is embodied as a Cu ball or as aconductive, compliant ball such as that described above, such a ball maybe affixed: (a) by re-flow after applying solder paste to the substrateand the Probe Card; (b) by curing after applying conductive paste to thesubstrate and the Probe Card; (c) by re-flow after applying conductivepaste to the substrate or the Probe Card and applying solder paste tothe Probe Card or the substrate, respectively; (d) and so forth. As astill further example, if the interconnector is embodied as a spring,such a spring may be affixed: (a) by re-flow after applying solder pasteto the substrate and the Probe Card; (b) by curing after applyingconductive paste to the substrate and the Probe Card; (c) by re-flowafter applying conductive paste to the substrate or the Probe Card andapplying solder paste to the Probe Card or the substrate, respectively;(d) and so forth.

[0040] In accordance with one or more still further embodiments of thepresent invention, the interconnectors may be eutectic solder balls thatare affixed by curing after applying conductive paste to the substrateand the Probe Card. For example, such a curing step will occur attemperatures in a range, for example and without limitation, from about120° C. to about 160° C., which range of temperatures is below themelting temperature (˜183° C.) of eutectic solder. Thus, in accordancewith such still further embodiments of the present invention, theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process. Further, as was explained above, because theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process, the distance between the substrate and theProbe Card may be determined by the size of the eutectic solder balls.

[0041] It should also be understood that further embodiments of thepresent invention exist wherein: (a) no interconnector alignment film isused; (b) an interconnector alignment film is applied to the Probe Card(see the above-described embodiment where the interconnector alignmentfilm is embodied as polyimide film 150); (c) an interconnector alignmentfilm may be applied to the substrate in a manner that will be readilyunderstood by one of ordinary skill in the art in light of thespecification; (d) and so forth.

[0042] In accordance with one or more embodiments of the presentinvention, when the interconnectors are short, structures fabricatedutilizing such interconnectors have short interconnection distances fromIC bumps under test to the Probe Card. For example, when interconnectorsare embodied as balls such as balls 181 and 182 described above having asolid Cu core with a diameter in a range, for example and withoutlimitation, from about 5 mils to about 10 mils, structures fabricatedutilizing such balls have interconnection distances from IC bumps undertest to the Probe Card that are short. Advantageously, the resultingstructures have electrical properties, such as, for example and withoutlimitation, line resistance, inductance, and so forth, that areimprovements over similar electrical properties for structures havinglonger interconnection distances.

[0043] An advantage provided by one or more of the above-describedembodiments of the present invention is that the substrate may beremoved from the Probe Card when the substrate becomes worn or isdamaged. For example, to do this, one would remove the Probe Card from aTester, de-solder the worn or damaged substrate utilizing any one of anumber of de-soldering methods that are well known to those of ordinaryskill in the art, and connect a new substrate to the Probe Card in itsplace. For example and without limitation, such a de-soldering methodmay include the use of forced hot air (the temperature being above themelting point of solder), and a suction to retrieve the substrate whenthe solder has melted to a sufficient degree. The new structure may thenbe replaced in the Tester.

[0044] The following describes another method (“Method II”) forconnecting a substrate to a Probe Card (i.e., for connecting BGA pads ofa substrate to BGA pads of a Probe Card) in accordance with one or moreembodiments of the present invention wherein, in accordance with Part Iof Method II, interconnectors are connected to the substrate before thesubstrate is connected to the Probe Card, which substrate can be, forexample and without limitation, a rigid substrate, a flex substrate, ora semi-flex substrate.

[0045] In a first, optional step of Part I of Method II, a release film(such as, for example and without limitation, a release film like thatdescribed above in conjunction with Method I) is aligned with, andplaced over, a base plate of a pinalignment fixture (such as, forexample and without limitation, a base plate and a pinalignment fixturelike those described above in conjunction with Method I). Next, asubstrate is aligned with, and placed over, the release film on thepinalignment fixture with its BGA pad side up. Next, a paste stencilmask that is fabricated in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art isaligned with, and placed over, the substrate on the pinalignmentfixture. Next, a paste such as, for example and without limitation, aflux or a no-clean solder paste is applied onto the BGA pads of thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art such as, for example and withoutlimitation, methods utilizing a dispensing machine, methods utilizingscreen-printing, methods utilizing a squeegee, and so forth. Also, inaccordance with one or more further embodiments of the presentinvention, the paste may be any one of a number of conductive pastesthat are well known to those of ordinary skill in the art such as, forexample, and without limitation, a Ag conductive paste, a Au conductivepaste, a Cu conductive paste, and so forth, or it may be any one of anumber of solder pastes that are well known to those of ordinary skillin the art. Further, the paste can be a compliant, conductive pastewhere such compliant conductive paste may be any one of a number of suchproducts that are well known to those of ordinary skill in the art suchas, for example and without limitation, an elastomer such as a siliconeelastomer having conductive particles embedded therein. The use of acompliant conductive paste may be advantageous in that the resultingstructure may be able to take up vertical movements or movements in aZ-direction caused during testing by non-planarity of contactors on thesubstrate, pads on the substrate, pads on the Probe Card, and/or I/Ocontacts on the wafer. Next, the paste stencil mask is removed.

[0046] Next, a stencil (such as, for example and without limitation, astencil like that described above in conjunction with Method I toposition balls) is aligned with, and placed over, the substrate on thepinalignment fixture; the edges of the stencil could have a corralformed thereon (such as, for example and without limitation, a corrallike that described above in conjunction with Method I). Next, ballshaving a rigid core and a solder coating (such as, for example andwithout limitation, balls like those described above in conjunction withMethod I) are placed over the stencil, and the stencil is removed. Next,the solder coating on the balls is re-flowed (in a re-flow step such as,for example and without limitation, a re-flow step like that describedabove in conjunction with Method I). The resulting piece may beinspected, and re-work may take place if necessary. As one can readilyappreciate from the above, Part I of Method II may be utilized, amongother things, to prepare a replacement substrate for connection to aProbe Card by affixing balls to the BGA pads thereof.

[0047] It should be understood by those of ordinary skill in the artthat the balls utilized in the above-described embodiment of the presentinvention are interconnectors that provide electrical continuity betweenpads on the bottom or non-testing side of the substrate and pads on thetop side of the Probe Card. In general, the interconnectors may be anytype of electrical conductor (for example and without limitation, it iscomprised of an electrical conducting material): (a) whose electricalconductivity is sufficient to satisfy design electrical requirements ofa resulting structure or lay-up; and (b) that has at least a core thatdoes not melt as a result of applying heat during the fabricationprocess. For example and without limitation, the core does not melt attemperatures used to re-flow eutectic solder (for example, temperaturesin a range from about 183° C. (the melting point of eutectic solder) toabout 230° C.). Thus, for this case, for example, and withoutlimitation, the core may be a material that melts at a temperature thatis higher than 230° C. since such a material would not melt in thespecified range. In light of this, when the interconnectors are embodiedas balls, such balls may be: (a) solid Cu balls; (b) solid Cu balls thatare coated with eutectic solder; (c) solid Indium alloy balls; (d) solidIndium alloy balls that are coated with solder; (e) solid high leadsolder (for example and without limitation, 97/3 or 95/5) balls; (f)solid high lead solder (for example and without limitation, 97/3 or95/5) balls that are coated with solder; and (g) so forth. In addition,further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) is notsolid, and further embodiments can be fabricated wherein the core of theinterconnectors (for example and without limitation, balls) comprises aceramic material that is embedded with a conducting material such as,for example, and without limitation, gold, Cu, silver, Indium, Ni, andso forth. Embodiment of such balls may be fabricated in accordance withany one of a number of methods that are well known to those of ordinaryskill in the art, and one or more embodiments of such balls arecommercially available.

[0048] In accordance with one or more further embodiments of the presentinvention, the interconnectors may be compliant conductive balls, forexample and without limitation, compliant conductive plastic balls. Forexample, suitable conductive, compliant balls are commercially availablethat have a plastic core (for example and without limitation, a plasticcore having a hollow center), which plastic core is surrounded or coatedwith: (a) a layer of Cu; (b) a layer of Cu and a layer of Ni; (c) alayer of Cu, a layer of Ni, and a layer of Au; (d) one or more of alayer of Cu; a layer of Ni; and a layer of Au; and (e) so forth. Inaddition, in accordance with one or more still further embodiments ofthe present invention, the interconnectors may be springs (suitablesprings may be obtained commercially).

[0049] It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art. For example and withoutlimitation, if an interconnector is embodied as a solder coated Cu ball,such a solder coated ball may be affixed to the substrate: (a) byre-flow; (b) by re-flow after applying flux to the substrate; (c) byre-flow after applying conductive paste to the substrate; and (d) soforth. As a further example, if an interconnector is embodied as a Cuball or as a conductive, compliant ball such as that described above,such a ball may be affixed to the substrate: (a) by re-flow afterapplying solder paste to the substrate; (b) by curing after applyingconductive paste to the substrate; and (c) so forth. As a still furtherexample, if the interconnector is embodied as a spring, such a springmay be affixed to the substrate: (a) by re-flow after applying solderpaste to the substrate; (b) by curing after applying conductive paste tothe substrate; and (c) so forth.

[0050] It should also be understood that further embodiments of thepresent invention exist wherein: (a) no interconnector alignment film isused; or (b) an interconnector alignment film is applied to thesubstrate in a manner that will be readily understood by one of ordinaryskill in the art in light of the specification.

[0051] The following describes Part II of Method II, i.e., a method forconnecting a structure having balls affixed to the BGA pads thereto tothe Probe Card. In a first, optional step of Part II of Method II, arelease film (such as, for example and without limitation, a releasefilm like that described above in conjunction with Method I) is alignedwith, and placed over, a base plate of a pinalignment fixture (such as,for example and without limitation, a base plate and a pinalignmentfixture like those described above in conjunction with Method I). Next,the Probe Card is aligned with, and placed over, the release film on thepinalignment fixture. Next, a paste stencil mask (such as, for exampleand without limitation, a paste stencil mask like that described abovein conjunction with Part I of Method II) is aligned with, and placedover the Probe Card on the pinalignment fixture. Next, a paste (such as,for example and without limitation, a paste like that described above inconjunction with Part I of Method II) is applied onto the pads of theProbe Card (in a paste application step such as, for example and withoutlimitation, a paste application step like that described above inconjunction with Part I of Method II). Next, the paste stencil isremoved.

[0052] Next, the substrate, with the balls facing down, is aligned with,and placed over the Probe Card on the pinalignment fixture. Next, in anoptional step, a release film (such as, for example and withoutlimitation, a release film like that described above in conjunction withPart I of Method II) is aligned with, and placed over, the structure onthe pinalignment fixture. Next, a weight (such as, for example andwithout limitation, a weight like that described above in conjunctionwith Method I) is aligned with, and placed over, the release film on thepinalignment fixture. Next, the solder coating on the balls is re-flowed(in a re-flow step such as, for example and without limitation, are-flow step like that described above in conjunction with Part I ofMethod II). During the re-flow process, the weight provides a force thatcauses the solder to flow so that the distance between the substrate andthe Probe Card is determined by a dimension of the core of the balls(for example and without limitation, the diameter of the core). Itshould be understood that other mechanisms for applying a force (i.e.,other than the weight) that causes the solder to flow so that thedistance between the substrate and the Probe Card is determined by thediameter of the core of the balls may be used to fabricate one or morefurther embodiments of the present invention such as, for example andwithout limitation, by the use of springs that are adapted to urge thesubstrate and the Probe Card towards each other. Finally, the structureor lay-up comprised of the connected substrate and Probe Card is removedfrom the pinalignment fixture, and the release films are removed. In analternative embodiment of Part II of Method II, a support film such as,for example and without limitation, a polyimide film, may be placed overthe Probe Card before the paste is applied to help support the ballsduring testing. In addition, a stiffening mechanism like that describedabove may be (optionally) connected to a side of the Probe Card oppositefrom the side to which the substrate is connected.

[0053] It should be understood that further embodiments of the presentinvention exist wherein the interconnectors may be affixed to the ProbeCard utilizing any one of a number of methods that are well known tothose of ordinary skill in the art. For example and without limitation,if an interconnector is embodied as a solder coated Cu ball, such asolder coated ball may be affixed to the Probe Card: (a) by re-flow; (b)by re-flow after applying flux to the Probe Card; (c) by re-flow afterapplying conductive paste to the Probe Card; and (d) so forth. As afurther example, if an interconnector is embodied as a Cu ball or as aconductive, compliant ball such as that described above, such a ball maybe affixed to the Probe Card: (a) by re-flow after applying solder pasteto the Probe Card; (b) by curing after applying conductive paste to theProbe Card; and (c) so forth. As a still further example, if theinterconnector is embodied as a spring, such a spring may be affixed tothe Probe Card: (a) by re-flow after applying solder paste to the ProbeCard; (b) by curing after applying conductive paste to the Probe Card;and (c) so forth.

[0054] In accordance with one or more still further embodiments of thepresent invention, the interconnectors may be eutectic solder balls thatare affixed by curing after applying conductive paste to the substrateand the Probe Card. For example, relevant curing steps will occur attemperatures in a range, for example and without limitation, from about120° C. to about 160° C., which range of temperatures is below themelting temperature (˜183° C.) of eutectic solder. Thus, in accordancewith such still further embodiments of the present invention, theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process. Further, as was explained above, because theeutectic solder ball will not melt as a result of applying heat duringthe fabrication process, the distance between the substrate and theProbe Card may be determined by the size of the eutectic solder balls.

[0055] The following describes another method (“Method III”) forconnecting a structure comprised of at least two substrates to a ProbeCard (i.e., for connecting BGA pads of the structure comprised of atleast two substrates to BGA pads of the Probe Card) in accordance withone or more embodiments of the present invention. Due to limitations inwiring density for substrates presently available in the market, forhigh I/O chip applications (for example and without limitation, chipapplications involving over 3,000 I/O connections) the wiring densitymay be insufficient to wire all contactors from the top or testingsurface of a substrate through to the other side to pads that are to beconnected to a Probe Card. Thus, for example and without limitation, insuch high I/O chip applications, a substrate having contactors that facea wafer might be fanned-out to another substrate that is sometimesreferred to as a second level substrate. Then, in accordance with one ormore embodiments of the present invention, a first substrate havingcontactors for use in testing a circuit is connected to a secondsubstrate using interconnectors such as, for example and withoutlimitation, any of the interconnectors described above in conjunctionwith Methods I or II; and the two substrates are connected utilizing anyof the embodiments described above in conjunction with Method I orMethod II. Next, the structure comprised of the two substrates may beconnected to the Probe Card utilizing any of the embodiments describedabove in conjunction with Method I or Method II. In addition, astiffening mechanism like that described above may be (optionally)connected to a side of the Probe Card opposite from the side to whichthe substrate is connected.

[0056] The following describes another method (“Method IV”) forconnecting a flexible substrate (sometimes referred to as a “flexsubstrate”) to a Probe Card (i.e., for connecting BGA pads of the flexsubstrate to BGA pads of the Probe Card) in accordance with one or moreembodiments of the present invention. A suitable flex substrate may befabricated from polyimide or from any other suitable materials that arewell known to those of ordinary skill in the art. In accordance with oneor more such embodiments, the flex substrate has a thickness in a rangefrom, for example and without limitation, about 1 mil to about 3 mils toprovide a predetermined degree of flexibility. The degree of flexibilitythat may be utilized in a particular application may be determined, forexample and without limitation, readily by one of ordinary skill in theart without undue experimentation by testing.

[0057]FIG. 2 is a top view that shows a portion of flex substrate 175that is fabricated in accordance with one or more embodiments of thepresent invention. As shown in FIG. 2, and in accordance with one ormore such embodiments of the present invention, the BGA pads on thebottom or non-testing side of flex substrate 175 (i.e., the sideopposite contactors 177 ₁-177 ₆) is laid out in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art so that the following is true for a predetermined fraction ofthe BGA pads for a particular grid, for example and without, a 0.8 mmgrid or a 0.65 mm grid. An area surrounded by pads 179 ₁-179 ₄ (shown inphantom in FIG. 2) encompasses contactors 177 ₁-177 ₆. Next, inaccordance with one or more such embodiments of the present invention,the substrate is connected to the Probe Card using interconnectors suchas, for example and without limitation, any of the interconnectorsdescribed above in conjunction with Methods I or II; and the substrateand the Probe Card are connected utilizing any of the embodimentsdescribed above in conjunction with Method I or Method II.Advantageously, in accordance with one or more such embodiments of thepresent invention, during use in a Tester or Test System, the flexsubstrate acts like a drum membrane. As a result, whenever a structurefabricated in accordance with this embodiment of the present inventionis used in a Tester, the contactors are able to move distances that makeup for at least some non-planarity in the structure itself, and/or forany non-uniformity in bump height on the wafer.

[0058] The following describes another method (“Method V”) forconnecting a substrate to a Probe Card (i.e., for connecting BGA pads ofa substrate to BGA pads of a Probe Card) in accordance with one or moreembodiments of the present invention, which substrate can be, forexample and without limitation, a rigid substrate, a flex substrate, ora semi-flex substrate.

[0059] In a first step of Method V, a thickness of at least two edges ofa substrate such as, for example and without limitation, a rigidsubstrate, is reduced by use of any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, using a router, a laser, and so forth to formbevels. FIGS. 3-5 are cross sectional views that show substrates 186,187, and 188, respectively, that have bevels formed on the edges ofthereof in accordance with one or more embodiments of the presentinvention. In accordance with one such embodiment, the thickness of theedge of the substrate is reduced to a thickness in a range, for exampleand without limitation, from about 0.2 mm to about 0.3 mm.

[0060] Next, compliant interconnectors such as, for example and withoutlimitation, compliant, conductive balls or springs (such as, for exampleand without limitation, compliant, conductive balls or springs likethose described above in conjunction with Methods I or II) are connectedto the substrate utilizing any of the embodiments described above inconjunction with Part I of Method II.

[0061] Next, an optional interconnector alignment film (for example andwithout limitation, a polyimide film like that described above havingholes in it that align to the Probe Card pads), may be affixed to theProbe Card utilizing methods described above in conjunction with, forexample, Method I. Such an interconnector alignment film would act as aguide for the balls or springs.

[0062] Next, electrical connection between pads on the substrate andpads on the Probe Card is provided by a clamp mechanism shown in FIG. 6.As shown in FIG. 6, the clamp mechanism includes: (a) substrate cover310; (b) a connection mechanism shown, for example and withoutlimitation, as a releasable connection mechanism comprised of screws 305₁-305 ₄ and nuts 307 ₁-307 ₄; and (c) guide pins 320 ₁-320 ₄. As shownin FIG. 6, guide pins 320 ₁-320 ₄ are used to align the substrate toholes 325 ₁-325 ₄ in Probe Card 330, and to align substrate cover 310over the substrate so that the balls or springs connected to thesubstrate are aligned with pads on Probe Card 330. As further shown inFIG. 6, substrate cover 310 includes a recess that is formed by lip 327.As further shown in FIG. 6, area 329 of the recess in substrate cover310 is open to enable access to contactors disposed on a top side of thesubstrate during testing. In addition, lip 327 of substrate cover 310 isformed so that it fits over the beveled edges of the substrate to holdthe substrate in place when the structure is assembled. Guide pins 320₁-320 ₄ are removed after substrate cover 310 is connected to Probe Card330 using, for example and without limitation, a connection mechanism,for example and without limitation, a releasable connection mechanismcomprised of screws 305 ₁-305 ₄ and nuts 307 ₁-307 ₄. In accordance withone or more such embodiments, electrical contact is ensured by pressureapplied by the wafer during testing. In addition, a stiffening mechanismlike that described above may be (optionally) connected to a side of theProbe Card opposite from the side to which the substrate is connected.It should be understood that in one or more alternatives of theabove-described embodiment, the substrate may not have bevels formed inthe sides, and lip 327 of substrate cover 310 is formed so that it fitsover the edges of the substrate to hold the substrate in place when thestructure is assembled.

[0063] In accordance with one or more further alternatives of theabove-described embodiment, instead of connecting the conductive,compliant balls or springs to the substrate (as described above), theyare connected to Probe Card 330 using the same steps set forth above forconnecting the conductive, compliant balls or springs to the substrate.In accordance with such further alternative embodiments, a polyimidefilm may be applied to the Probe Card to support the balls or springs aswas done in Method I, however, this is not necessary. Next, electricalconnection between pads on the substrate and pads on the Probe Card isprovided by using the clamp mechanism shown in FIG. 6. In either case,if the substrate wears out or, is damaged, it is easily replaced byreleasing the connection mechanism, for example and without limitation,by removing screws 305 ₁-305 ₄, thereby causing minimum equipmentdowntime. Advantageously, compliant balls or springs may make up for atleast some non-planarity in the structure itself, and/or for anynon-uniformity in bump height on the wafer.

[0064] The following describes another method (“Method VI”) forconnecting a substrate to a Probe Card (i.e., for connecting BGA pads ofa substrate to BGA pads of a Probe Card) in accordance with one or moreembodiments of the present invention. In accordance with one or moreembodiments of the present invention, the substrate is a chip havingspring-type contactors on a testing side, which chip is fabricated, forexample and without limitation, using standard MEMS technology. Inaccordance with one or more such embodiments, each contactor is wiredthrough vias on the chip to make contact with pads on the bottom side ofthe chip in accordance with any one of a number of methods that are wellknown to those of ordinary skill in the art. Advantageously, the springtype contactors on the top of the chip make up for at least somenon-planarity in the structure itself, and/or for any non-uniformity inbump height on the wafer. The chip may be connected to the Probe Cardusing any one of the above-described embodiments. For example, FIG. 7 isa cross sectional view that shows chip substrate 360 that is fabricatedin accordance with one or more embodiments of the present invention. Asshown in FIG. 7, chip substrate 360 includes bevels 361 ₁-361 ₂;alignment vias 367 ₁-367 ₂; spring-type contactors 363 ₁-363 ₂; wiring369 ₁-369 ₂; and pads 367 ₁-367 ₂ to enable use of one or moreembodiments of Method V above.

[0065] The following describes another method (“Method VII”) forconnecting a substrate to a Probe Card (i.e., for connecting BGA pads ofa substrate to BGA pads of a Probe Card) to provide an inventivestructure in accordance with one or more embodiments of the presentinvention. In accordance with one or more such embodiments, theinventive structure comprises a substrate, a Probe Card, and aninterconnector in the form of a connector-holder that is aligned to thesubstrate and the Probe Card, wherein electrical connections betweenpads on the substrate and pads on the Probe Cards are made through theconnector-holder utilizing electrical connectors such as, for exampleand without limitation, electrical connectors having first and secondretractable ends (for example, Pogo pins). Advantageously, in accordancewith one or more such embodiments of the present invention, inventivestructures are produced that may be used cost effectively for testingbecause, among other reasons, the substrate may be replaced easily andrapidly with a new one when the substrate is damaged or worn.

[0066] In accordance with one or more embodiments of the presentinvention, a flexible, HDI substrate is fabricated utilizing, forexample and without limitation, polyimide, Teflon, and so forth inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art. In accordance with one or more suchembodiments of the present invention, the substrate has a thickness in arange, for example and without limitation, from about 2 mils to about 3mils, and the substrate has contactors disposed on a top side of thesubstrate in an array that has the same pitch as that of bumps on a chipon a wafer to be tested. The contactors are wired through vias inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art, and the wires contact BGA padsdisposed on a bottom side of the substrate, which BGA pads are disposedin a grid array that has a predetermined grid array spacing, for exampleand without limitation, a spacing in a range from about 0.65 mm to about1.27 mm. Although it is not required to utilize a flex substrate tocarry out Method VII, one advantage of using a flex substrate is thatthe resulting structure may make up for at least some non-planarity inthe structure itself, and/or for any non-uniformity in bump height onthe wafer. This is because movement in a Z-axis (i.e., an axisperpendicular to a plane of the substrate) is provided by the flexsubstrate, with or without the need for compliant connectors disposedbetween it and the Probe Card.

[0067] In accordance with Part I of Method VII, a connector-holder isfabricated. In accordance with one or more such embodiments, theconnectors are electrical connectors having first and second retractableends (for example, Pogo pins), and the connector-holder for these Pogopins is fabricated from plastic such as, for example and withoutlimitation, ULTEM™, Torlon, and so forth. FIG. 8 shows Pogo pin 800 thatis commercially available from any one of a number of sources. As shownin FIG. 8, Pogo pin 800 includes plungers 810 and 811 and barrel 820.Pogo pin 800 provides an electrical conduit between the tips of plungers810 and 811, and as such, it is preferable that the tips of plungers 810and 811 of Pogo pin 800 be narrow to enable better electrical contactwith the pads. As such, plungers 810 and 811 may be fabricated, forexample and without limitation, of gold-plated hardened steel; barrel820 may be fabricated, for example and without limitation, of agold-plated copper alloy; and internal springs (not shown) may befabricated, for example and without limitation, of gold-plated pianowire.

[0068] The connector-holder comprises a connector-holder bottom plateand a connector-holder top plate that are both fabricated, for exampleand without limitation, from plastic. FIG. 9 is a top perspective viewthat shows connector-holder bottom plate 600 that is fabricated inaccordance with one embodiment of the present invention, and FIG. 10 isa bottom perspective view that shows connector-holder top plate 700 thatis fabricated in accordance with one embodiment of the presentinvention. Connector-holder bottom plate 600 and connector-holder topplate 700 may be fabricated in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by injection molding, and holesmay be fabricated therein in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by drilling. Referring to FIG.9, the locations of the holes in array 610 of connector-holder bottomplate 600 match the locations of BGA pads on the Probe Card. Further,referring to FIG. 10, the locations of the holes in array 710 ofconnector-holder top plate 700 match the locations of BGA pads on thesubstrate. Still further, in accordance with one or more embodiments ofthe present invention, the holes in array 610 of connector-holder bottomplate 600 (such as hole 615 shown in FIG. 11) comprise hole 616 withinhole 617 for retaining Pogo pins in place when connector-holder bottomplate 600 and connector-holder top plate 700 are connected. For example,(a) the diameter of hole 616 is larger—preferably by a small amount—(forexample and without limitation, the diameter of hole 616 is in a rangefrom about 1 mil to about 3 mils) than the diameter of plunger 810 ofPogo pin 800 shown in FIG. 8; and (b) the diameter of hole 617larger—preferably by a small amount—than the diameter of barrel 820 ofPogo pin 800. Yet still further, in accordance with one or moreembodiments of the present invention, the holes in array 710 ofconnector-holder top plate 700 (such as hole 715 shown in FIG. 12)comprise hole 716 within hole 717 for retaining Pogo pins in place whenconnector-holder bottom plate 600 and connector-holder top plate 700 areconnected. For example, the (a) the diameter of hole 716 islarger—preferably by a small amount—than the diameter of plunger 811 ofPogo pin 800; and (b) the diameter of hole 717 is larger—preferably by asmall amount—than the diameter of barrel 820 of Pogo pin 800.

[0069] As shown in FIG. 9, connector-holder bottom plate 600 includesposts 611 ₁-611 ₄. Posts 611 ₁-611 ₄ include holes for connectionmechanisms (for example and without limitation, releasable connectionmechanisms) comprised, for example and without limitation, of screws 937₁-937 ₄ (shown in FIG. 13) that are used to hold connector-holder bottomplate 600 and connector-holder top plate 700 together (as will bedescribed below). As further shown in FIG. 10, connector-holder topplate 700 includes receptacles 711 ₁-711 ₄. Receptacles 711 ₁-711 ₄include holes for the connection mechanisms (for example and withoutlimitation, releasable connection mechanisms) comprised, for example andwithout limitation, of screws 937 ₁-937 ₄ (shown in FIG. 13) that areused to hold connector-holder bottom plate 600 and connector-holder topplate 700 together (as will be described below). The shape ofreceptacles 711 ₁-711 ₄ is such that posts 611 ₁-611 ₄, mate withreceptacles 711 ₁-711 ₄ when connector-holder bottom plate 600 andconnector-holder top plate 700 are connected to each other. As stillfurther shown in FIG. 10, connector-holder top plate 700 furtherincludes: (a) vias 712 ₁-712 ₄ that are used for guide pins 910 ₁-910 ₄(shown in FIG. 13); and (b) holes 713 ₁-713 ₄ that are used forconnection mechanisms (for example and without limitation, releasableconnection mechanisms) comprised, for example and without limitation, ofscrews 940 ₁-940 ₄ (shown in FIG. 13) to hold the connector-holder inplace after final assembly (as will be described below).

[0070] To assemble the connector-holder in accordance with one or moreembodiments of the present invention: (a) Pogo pins are placed into theholes of array 710 of connector-holder top plate 700; (b)connector-holder bottom plate 600 is then placed over connector-holdertop plate 700; and (c) as indicated in FIG. 13, connector-holder bottomplate 600 is connected to connector-holder top plate 700 by screwingconnector-holder bottom plate 600 into connector-holder top plate 700 atfour (4) corners using screws 937 ₁-937 ₄.

[0071] In accordance with Method VII, vias are formed for guide pins 910₁-910 ₄ (shown in FIG. 13) in the substrate and the Probe Card inaccordance with any one of a number of methods that are well known tothose of ordinary skill in the art.

[0072]FIG. 13 is an exploded view that shows a portion of a structureused to test circuits that is fabricated in accordance with one or moreembodiments of the present invention. Clamp 930 (a bottom perspectiveview of clamp 930 is shown in FIG. 13) includes: (a) vias 965 ₁-965 ₄that are used for guide pins 910 ₁-910 ₄ (shown in FIG. 13); and (b)holes 961 ₁-961 ₄ that are used for screws 940 ₁-940 ₄ (shown in FIG.13) to hold the connector-holder and the substrate in place on ProbeCard 920 (as will be described below). As shown in FIG. 13, clamp 930includes a recess that is formed by lip 978. As further shown in FIG.13, area 987 of the recess in clamp 930 is open to enable access tocontactors disposed on a top side of the substrate during testing. Inaddition, lip 978 is formed so that it fits over, and may make contactwith the edges or any bevels in the edges, of the substrate when thestructure is assembled. Clamp 930 is fabricated, for example and withoutlimitation, from plastic in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by injection molding, and holesmay be fabricated therein in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by drilling.

[0073] In accordance with one embodiment of Part II of Method VII, thesubstrate is connected to the connector-holder fabricated in accordancewith Part I of Method VII. In a first optional step of this embodimentof Part II of Method VII, a thickness of at least two edges of asubstrate is reduced by use of any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, using a router, a laser, and so forth to formbevels like those fabricated in accordance with Method V. The thicknessof the routed edges is a function of the Z-movement of the Pogo pinsused to fabricate the connector-holder described above.

[0074] Next, in another optional step of this embodiment of Part II ofMethod VII, a release film such as, for example and without limitation,a release film like that described above in conjunction with Method I)is aligned with, and placed over, a base plate of a pinalignment fixture(such as, for example and without limitation, a base plate and apinalignment fixture like those described above in conjunction withMethod I). Next, a substrate is aligned with, and placed over, therelease film on the pinalignment fixture with its BGA pads side up.Next, a paste stencil mask that is fabricated in accordance with any oneof a number of methods that are well known to those of ordinary skill inthe art is aligned with, and placed over, the substrate on thepinalignment fixture. Next, a paste such as, for example and withoutlimitation, a no-clean solder paste is applied onto the BGA pads of thesubstrate utilizing any one of a number of methods that are well knownto those of ordinary skill in the art such as, for example and withoutlimitation, methods utilizing a dispensing machine, methods utilizingscreen-printing, methods utilizing a squeegee, and so forth. Also, inaccordance with one or more further embodiments of the presentinvention, the paste may be any one of a number of conductive pastesthat are well known to those of ordinary skill in the art such as, forexample, and without limitation, a Ag conductive paste, a Au conductivepaste, a Cu conductive paste, and so forth, or it may be any one of anumber of solder pastes that are well known to those of ordinary skillin the art. Further, the paste can be a compliant, conductive pastewhere such compliant conductive paste may be any one of a number of suchproducts that are well known to those of ordinary skill in the art suchas, for example and without limitation, an elastomer such as a siliconeelastomer having conductive particles embedded therein. Next, the pastestencil mask is removed.

[0075] Next, in accordance with this embodiment of Part II of MethodVII, a connector-holder fabricated in accordance with Part I of MethodVII is pinaligned (using two or more of guide pins 910 ₁-910 ₄ shown inFIG. 13) to the substrate fabricated in accordance with Part II ofMethod VII. Next, the resulting substrate structure is re-flowed orcured, depending on the type of paste used, to connect the Pogo pins tothe BGA pads on the substrate.

[0076] Next, two or more of guide or dowel pins 910 ₁-910 ₄ are used toalign the resulting substrate structure with, and place the resultingsubstrate structure over, Probe Card 920 so that the tips of the Pogopins align with the pads on Probe Card 920. Finally, clamp 930 isaligned with, and placed over, Probe Card 920 utilizing two or more ofguide or dowel pins 910 ₁-910 ₄, and clamp 930 is connected to ProbeCard 920 utilizing screws 940 ₁-940 ₄ (screws 940 ₁-940 ₄ also passthrough the connector-holder) and nuts 950 ₁-950 ₄, thereby holding thefinal assembly in place. Alternatively, clamp 930 and theconnector-holder may be connected to Probe Card separately. Next, theguide pins are removed. In addition, a stiffening mechanism like thatdescribed above may be (optionally) connected to a side of the ProbeCard opposite from the side to which the substrate is connected.

[0077] Advantageously, using a flex substrate and Pogo pins inaccordance with the above-described embodiments enables bump heightnon-uniformity or non-planarity of the structure to be made up bymovement in a Z-axis during testing. Further, a short interconnectiondistance between the substrate and the Probe Card obtained from the useof small Pogo pins can create better electrical properties than those ofstructures produced using prior art methods. Still further, inaccordance with the above-described embodiments, whenever the flexsubstrate wears out or becomes damaged, the Pogo pins can be removedfrom it by de-soldering in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art. Thena new substrate may be incorporated into the assembly, and the ProbeCard may be reused.

[0078] In accordance with one or more alternative embodiments of MethodVII described above, the substrate is laid out in accordance with anyone of a number of methods that are well known to those of ordinaryskill in the art so that all the wiring to the bottom side of thesubstrate (i.e., the side opposite from the contactors) is routed to aperiphery of the substrate. As a result, in accordance with thisembodiment of the present invention, there are no pads underneathcontactors disposed in a region of the substrate, for example andwithout limitation, a center of the substrate. Next, a compliantsubstance such as, for example and without limitation, a compliantelastomer, is applied to the bottom side of the substrate, in thecentral area, in accordance with any one of a number of methods that arewell known to those of ordinary skill in the art such as, for exampleand without limitation, by screen printing or stenciling methods. Thecompliant substance would be thick enough so that it contactsconnector-holder top plate 700 when the substrate is connected to theconnector-holder as described above. Since the pads on the bottom sideof the substrate are on the periphery of the substrate, so too are thePogo pins held by the connector-holder disposed about the periphery ofthe substrate. As a result, whenever the contactors on the substratemove up and down during testing, the substrate can flex sufficiently tomake up for at least some non-planarity in the structure itself, and/orfor any non-uniformity in bump height on the wafer. In addition, inaccordance with one or more further such alternative embodiments, theconnector-holder has a hole in the middle, and the compliant substanceapplied to the bottom side of the substrate is made so thick that itextends through to the Probe Card, which Probe Card may also be milledto provide a recessed area into which the substance is seated.

[0079] The following describes another method (“Method VIII”) forconnecting a substrate to a Probe Card (i.e., for connecting BGA pads ofa substrate to BGA pads of a Probe Card) in accordance with one or moreembodiments of the present invention, which substrate can be, forexample and without limitation, a rigid substrate, a semi-rigidsubstrate, a silicon/glass substrate having MEMS-type springs, and soforth.

[0080] In accordance with Part I of Method VIII, an interconnector inthe form of a connector-holder is fabricated in accordance with Part Iof Method VII. Next, vias are formed for guide pins in the substrate andthe Probe Card in accordance with any one of a number of methods thatare well known to those of ordinary skill in the art.

[0081] Next, clamp 960 is fabricated, for example and withoutlimitation, from plastic in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by injection molding. Holes maybe fabricated in clamp 960 in accordance with any one of a number ofmethods that are well known to those of ordinary skill in the art suchas, for example and without limitation, by drilling. FIG. 15 is a topview that shows clamp 960. As shown in FIG. 15, clamp 960 includes: (a)vias 975 ₁-975 ₄ that are used for to guide pins (to be describedbelow); and (b) holes 971 ₁-971 ₄ that are used for connectionmechanisms, for example and without limitation, releasable connectionmechanisms comprised of screws, (to be described below) to connect clamp960 to the connector-holder. As further shown in FIG. 15, clamp 960includes stationary structures 981 ₁ and 981 ₂ which have lips (shown inphantom) that are disposed to cover a portion of the edges or any bevelsin the edges (see below) of the substrate and to engage (optional)grooves in the beveled edges of the substrate. As further shown in FIG.15, clamp 960 includes a substrate alignment mechanism. In particular,as further shown in FIG. 15, clamp 960 includes laterally movablestructures 981 ₃ and 981 ₄ which have lips (shown in phantom) that aredisposed to cover at least a portion of the beveled edges (see below) ofthe substrate and to engage (optional) grooves in the beveled edges ofthe substrate. As further shown in FIG. 15, clamp 960 includes springs991 ₁ and 991 ₂ and springs 991 ₃ and 991 ₄. Springs 991 ₁ and 991 ₂urge movable structure 981 ₃ toward the center of clamp 960, and springs991 ₃ and 991 ₄ urge movable structure 981 ₄ toward the center of clamp960. In use, when clamp 960 is placed over the substrate (see below),stationary structures 981 ₁ and 981 ₂ and movable structures 981 ₃ and981 ₄ engage the edges of the substrate (for example and withoutlimitation, in grooves disposed therein), and springs 991 ₁, 991 ₂, 991₃, and 991 ₄ provide lateral forces that help align the substrate. Thoseof ordinary skill in the art should understand that (although theembodiment described above in conjunction with FIG. 15 indicated thatstructures 981 ₁ and 981 ₂ were stationary and that structures 981 ₃ and981 ₄ were laterally movable) further embodiments exist where all ofsome of structures 981 ₁-981 ₄ are movable. For example and withoutlimitation, in accordance with one or more further embodiments,structures 981 ₁ and 981 ₄ are movable and structures 981 ₂ and 981 ₃are stationary, or vice versa.

[0082] In accordance with Part II of Method VIII, first, (optionally) athickness of at least two edges of the substrate is reduced by use ofany one of a number of methods that are well known to those of ordinaryskill in the art such as, for example and without limitation, using arouter, a laser, and so forth to form bevels like those fabricated inaccordance with Method V. The thickness of the routed edges is afunction of the Z-movement of the Pogo pins used to fabricate theconnector-holder. Next, optional grooves, for example and withoutlimitation, V-shape grooves are cut into two or more sides of thesubstrate in accordance with any one of a number of methods that arewell known to those of ordinary skill in the art. FIG. 14 is a crosssectional view that shows an edge of the substrate with groove 657.

[0083] Next, guide or dowel pins are used to align the connector-holderwith the Probe Card (as a result, Pogo pins in the connector-holder areconnected to pads on the Probe Card). Once the connector-holder isaligned with respect to the Probe Card, the connector-holder isconnected to the Probe Card using a connection mechanism, for exampleand without limitation, a releasable connection mechanism comprised ofscrews and nuts. For example, four (4) screws are inserted through theconnector-holder and the Probe Card, and four (4) nuts are secured tothe screws to connect the connector-holder and the Probe Card. Next, theguide or dowel pins are removed. Next, the substrate is aligned with,and placed over, the connector-holder (two or more guide or dowel pinsare used to align the Pogo pins of the connector-holder with the BGApads of the substrate). Next, clamp 960 is aligned with, and placedover, the substrate (two or more guide or dowel pins are use to alignthe clamp and the substrate), and clamp 960 is connected to theconnector-holder using a connection mechanism, for example and withoutlimitation, a releasable connection mechanism comprised of screws. Forexample, four (4) screws are screwed into the connector-holder. Asdescribed above, clamp 960 confines vertical movement of the substrateas well as providing lateral alignment by spring action. In addition, astiffening mechanism like that described above may be (optionally)connected to a side of the Probe Card opposite from the side to whichthe substrate is connected. The Probe Card/substrate assembly is nowready for use in testing circuits.

[0084] In accordance with one or more further such embodiments of thepresent invention, a connector-holder is not fixedly connected to theProbe Card, and a clamp is connected directly to the Probe Card, whichclamp would include a connector-holder alignment mechanism and asubstrate alignment mechanism. For example and without limitation, inaccordance with such further embodiments, the connector-holder alignmentmechanism and the substrate alignment mechanism may be fabricatedutilizing movable structures and springs like those described above inconjunction with clamp 960.

[0085] In accordance with one or more such embodiments, advantageously,whenever the substrate wears out or becomes damaged, it is replacedwhile the Pogo pins stay in place and get reused. If a Pogo pin isdamaged, it can easily be pulled out of the connector-holder and bereplaced. Advantageously, since neither the connector-holder nor thePogo pins get replaced (unless a Pogo pin is damaged), there is minimumdowntime required for replacing the substrate. In addition, a shortinterconnection distance between the substrate and the Probe Cardobtained from the use of small Pogo pins can create better electricalproperties than those of structures produced using prior art methods.

[0086] Note that if one substrate is not sufficient to handle the wiringdensity required for a circuit or IC having lots of I/O (for example andwithout limitation, a circuit having >3000 I/O connections), a compositesubstrate may be fabricated which comprises a first level substrate anda second level substrate that is connected to the first level substrate.Electrical connection between the first level substrate and the secondlevel substrate can be made using any of the methods described aboveutilizing interconnectors such as, for example and without limitation,any of the interconnectors described above in conjunction with Methods Ior II; and the two substrates are connected utilizing any of theembodiments described above in conjunction with, for example and withoutlimitation, Method I or Method II. The composite substrate may then beconnected to the Probe Card utilizing any of the methods describedabove.

[0087] One or more further embodiments of the present invention relateto a Probe Card that can function as a universal Probe Card, i.e., aProbe Card that may be useful in a number of different testingapplications. In accordance with such one or more further embodiments,the Probe Card has a large number of pads disposed in a grid having, forexample and without limitation, at least about four hundred (400) padsand having, for example and without limitation, a 0.8 mm pad pitch. Asis well known, for a typical Probe Card, connections to analog I/O on achip are grouped and connected to one cluster of pins on the outside ofthe Probe Card, and connections to digital I/O on the chip are groupedand connected to another cluster of pins on the outside of the ProbeCard. Thus, in accordance with one such further embodiment of thepresent invention, the above described universal Probe Card wouldallocate a one fraction of its pads to analog I/O and another fractionof its pads to digital I/O. The allocation would be such that therewould be a sufficient number of connections to analog I/O and to digitalI/O to satisfy the required number of connections for a number ofdifferent chip designs. This would enable the Probe Card to be used in anumber of different testing applications. Then, in accordance with onesuch further embodiment of the present invention, a substrate specificto the particular chip being tested would be used with the universalProbe Card. Advantageously, the various specific substrates useful forthe various specific applications would be connected to the universalProbe Card utilizing one or more of the methods described herein.

[0088] One or more further embodiments of the present invention relateto a structure for testing circuits that is fabricated in accordancewith one or more embodiments of the present invention. FIG. 16 is across sectional view that shows structure 2001 that is fabricated inaccordance with one or more embodiments of the present invention. Asshown in FIG. 16, structure 2001 comprises substrate 2000, RF interfaceboard 2100, and Probe Card 2200. As further shown in FIG. 16, substrate2000 includes array 2010 of contactors on a top or testing side thereof(i.e., a side that contacts an IC on the wafer). As further shown inFIG. 16, RF interface board 2100 is connected, on a top side thereof, toBGA pads disposed on a bottom side of substrate 2000 by means of, forexample and without limitation, conductive balls 2020. As further shownin FIG. 16, RF interface board 2100 is further connected so that: (a)non-RF I/O BGA pads on a bottom side of RF interface board 2100 areconnected to BGA pads on a top side of Probe Card 2200 by means of, forexample and without limitation, conductive balls 2030, and (b) RFcoaxial cable connectors (not shown) on a bottom side of RF interfaceboard 2100 are connected to RF test coaxial cables 2110. As furthershown in FIG. 16, RF test coaxial cables 2110 are routed throughchannels 2220 in Probe Card 2200.

[0089]FIG. 17 is a top view that shows substrate 2000 and RF interfaceboard 2100 of structure 2001. As shown in FIG. 17, RF interface board2100 includes wing structures 2110 ₁-2110 ₄ (i.e., extension structureshaving perimeters wherein at least a portion of these perimeters extendbeyond a perimeter of substrate 2000). As further shown in FIG. 17, wingstructures 2110 ₁-2110 ₄ include wiring groups 2120 ₁-2120 ₄ (shown inphantom), respectively. In accordance with one or more embodiments ofthe present invention, wiring groups 2120 ₁-2120 ₄ provide electricalconnections from RF I/O BGA pads on a top side of RF interface board2100 to RF coaxial cable connectors (not shown) on a bottom side of RFinterface board 2100. In addition, RF interface board 2100 includeswiring (not shown) that provides electrical connections from non-RF I/OBGA pads on the top side of RF interface board 2100 to non-RF I/O BGApads on the bottom side of RF interface board 2100. RF interface board2100 maybe fabricated in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art usingmaterials utilized to fabricate a rigid substrate, a semi-flexsubstrate, a flex substrate, a silicon/glass structure, and so forth,and using any one of a number of RF coaxial cable connectors that arewell known to those of ordinary skill in the art. Note that although RFinterface board 2100 described above includes wing structures 2110₁-2110 ₄ shown in FIG. 17, further embodiments of the present inventionexist in which structures used to connect to RF I/O may take any one ofa number of forms such as, for example and without limitation, a singleboard whose periphery carries RF connectors, one or more wings, and soforth.

[0090] In use for testing, structure 2001 might be connected to, forexample and without limitation, a Pogo Tower (a Pogo Tower is a type ofconnector that is well known to those of ordinary skill in the art andwhich is used in some commercial test systems to provide an interface toa Probe Card). For example, in such an arrangement, a top side of thePogo Tower would be connected to non-RF test connectors 2210 (shown inFIG. 16) on a bottom side of Probe Card 2200 in a well known manner, anda bottom side of the Pogo Tower would be connected to a test systeminterface board in a well known manner. Further, RF test coaxial cables2110 (which are routed through channels 2220 in Probe Card 2200) wouldbe further routed through a central aperture in the Pogo Tower (manycommercial embodiments of a Pogo Tower are fabricated to have anaperture in the center), and would be connected directly to the testsystem interface.

[0091] In accordance with one or more such embodiments of the presentinvention, substrate 2000 may be any of the substrates that have beendescribed herein such as, for example and without limitation, a rigidsubstrate, a flex substrate, a semi-flex substrate, a silicon/glasssubstrate (for example and without limitation, a silicon/glass structurethat includes MEMS-type spring contactors), and so forth. In addition,Probe Card 2200 may be any one of a number of Probe Cards that are wellknown to those of ordinary skill in the art. Channels 2220 in Probe Card2200 may be fabricated in accordance with any one of a number of methodsthat are well known to those of ordinary skill in the art such as, forexample and without limitation, by drilling. Further, channels 2220 aremade large enough to enable the desired number of coaxial cables to fitthrough.

[0092] In fabricating structure 2001 described above, one may utilizeany of the above-described methods to connect substrate 2000 to RFinterface board 2100, and to connect RF interface board 2100 to ProbeCard 2200. Thus, as one can readily appreciate from the above, and inaccordance with one or more such embodiments of the present invention,the coaxial cables are connected close to contactors 2010, and the PogoTower is bypassed, thereby decreasing an electrical path betweencontactors on the substrate and the Test System. As a result, it isexpected that better electrical performance will be achieved when usingthe inventive structures when compared to that of structures fabricatedin accordance with the prior art.

[0093] One or more further embodiments of the present invention relateto a structure for testing circuits that is fabricated in accordancewith one or more embodiments of the present invention. FIG. 18 is across sectional view of structure 3000 that is fabricated in accordancewith one or more embodiments of the present invention. As shown in FIG.18, structure 3000 includes flex substrate 3010. Flex substrate 3010 isfabricated from any one of a number of flexible materials that are wellknown to those of ordinary skill in the art such as, for example andwithout limitation, polyimide, liquid crystal polymer (“LCP”), Teflon,and so forth. In addition, flex substrate 3010 has circuitry on bothsides, or is a multi-layer structure (for example and withoutlimitation, to provide a multi-level fan-out) depending on the amount ofI/O circuitry on a chip to be tested, which multilayer structure may befabricated in accordance with one or more of the methods describedherein. As shown in FIG. 18, flexible substrate 3010 has an array ofcontactors (for example, posts or bumps 3005 ₁-3005 ₂) located on a topor testing side (i.e., a side that contacts an IC on a wafer), whichcontactors make contact with bumped or non-bumped pads of a IC chip on awafer during testing. Posts or bumps on the top side of flex substrate3010 (for example, posts or bumps 3005 ₁-3005 ₂) are connected withtraces through flex substrate 3010 to pads (for example, pads 3015₁-3015 ₂) on the bottom side of flex substrate 3010. In accordance withone or more embodiments of the present invention, pads 3015 ₁-3015 ₂ areon the periphery of the array of contactors on the top side of flexsubstrate 3010, i.e., pads 3015 ₁-3015 ₂ are not under posts or bumps3005 ₁-3005 ₂. Posts or bumps 3005 ₁-3005 ₂ may have a height, forexample and without limitation, in a range from about 40 μm to about 60μm. Further, the posts or bumps on the top side of flex substrate 3010,the traces, and the pads on the bottom side of flex substrate 3010 maybe fabricated using any one of a number of methods that are well knownto those of ordinary skill in the art. For example and withoutlimitation, the pads (for example, pads 3015 ₁-3015 ₂) on the bottomside of flex substrate 3010 may be fabricated from alloys such asCu/Ni/Au, Ni/Au and so forth.

[0094] As further shown in FIG. 18, substrate 3020 is a rigid substrate.In accordance with one or more embodiments of the present invention,substrate 3020 has no circuitry. Substrate 3020 may be fabricated, forexample and without limitation, from FR-4 glass epoxy substrates, BTepoxy materials, and so forth, and may have a thickness in a range, forexample and without limitation, from about 0.5 mm to about 1.5 mm. Inaccordance with one or more embodiments of the present invention, thearea of substrate 3020 (in a plane perpendicular to the plane of FIG.18) is larger than the area of flex substrate 3010 (also in a planeperpendicular to the plane of FIG. 18). As further shown in FIG. 18,substrate 3020 includes vias (for example, vias 3027 ₁-3027 ₂) in anarray whose locations are aligned with the locations of the pads (forexample, pads 3015 ₁-3015 ₂) on the bottom side of flex substrate 3010.The vias (for example, vias 3027 ₁-3027 ₂) surround at least a portionof a barrel of electrical connectors having first and second retractableends such as, for example and without limitation, Pogo pins (forexample, Pogo pins 3030 ₁-3030 ₂), wherein the diameter of the vias is afunction of the diameter of the barrel of the Pogo pins. The Pogo pinsshown in FIG. 18 (for example, Pogo pins 3030 ₁-3030 ₂) are like Pogopin 800 described above. As further shown in FIG. 18, the vias (forexample, vias 3027 ₁-3027 ₂) are disposed so that retractable ends ofthe Pogo pins (for example, Pogo pins 3030 ₁-3030 ₂) contact pads (forexample, pads 3015 ₁-3015 ₂) on the bottom side of flex substrate 3010when structure 3000 is assembled in the manner described herein.

[0095] As further shown in FIG. 18, compliant adhesive layer 3040includes vias that are aligned with the pads (for example, pads 3015₁-3015 ₂) on the bottom side of flex substrate 3010. Compliant adhesivelayer 3040 may be fabricated using any one of a number of materials thatare well known to those of ordinary skill in the art such as, forexample and without limitation, a silicon elastomer, a flexible epoxy,and so forth.

[0096] A pinalignment fixture like that described above may be used in afirst stage of a method for assembling structure 3000. In a first,optional step, a release film such as, for example and withoutlimitation, a Mylar film or a Teflon film, is aligned with, and placedover, a base plate of the pinalignment fixture (as was described above,holes in the release film match the positions of alignment pins). Next,flex substrate 3010 is aligned with, and placed over, the release filmon the pinalignment fixture (holes in flex substrate 3010 (not shown)match the positions of the alignment pins). Next, compliant adhesivelayer 3040 is aligned with, and placed over flex substrate 3010 on thepin alignment structure (holes in compliant adhesive layer 3040 (notshown) match the positions of the alignment pins). Next, rigid substrate3020 is aligned with, and placed over compliant adhesive layer 3040(holes in rigid substrate 3020 (not shown) match the positions of thealignment pins). Next, a weight, for example, an aluminum or stainlesssteel plate having a thickness in a range, for example and withoutlimitation, from about 10 mm to about 12.7 mm, and having an area ofabout the same size as that of compliant adhesive layer 3040, is alignedwith, and placed over rigid substrate 3020 to apply pressure tocompliant adhesive layer 3040 (holes in the weight match the positionsof the alignment pins). Next, flex substrate 3010 may be laminated torigid substrate 3020 by, for example and without limitation, baking inan oven. The oven temperature may be in a range, for example and withoutlimitation, from about 150° C. to about 200° C., the pressure exerted bythe weight may be in a range, for example and without limitation, fromabout 14 kg/cm² to about 28 kg/cm², and the time spent in the oven maybe in a range, for example and without limitation, from about 1 hour toabout 2 hours. Next, the intermediary structure is removed from thepinalignment structure.

[0097] As further shown in FIG. 18, socket interposer 3050 is formed,for example and without limitation, from plastic such as ULTEM™, Torlon,and so forth. Socket interposer 3050 includes holes (for example, holes3045 ₁-3045 ₂) in an array whose locations are aligned with thelocations of the pads (for example, pads 3015 ₁-3015 ₂) on the bottomside of flex substrate 3010. As further shown in FIG. 18, each of theholes in socket interposer 3050 (for example, holes 3045 ₁-3045 ₂)comprises a hole within a hole for seating the Pogo pins (for example,Pogo pins 3030 ₁-3030 ₂) when structure 3000 is assembled in the mannerdescribed herein (also refer to the discussion of connector-holderbottom plate 600 above in conjunction with FIG. 11 to understand themanner in which such holes retain Pogo pins). Note that one or morealternative embodiments may not utilize the hole within a hole seatingmechanism.

[0098] As further shown in FIG. 18, socket interposer 3050 alsoincludes: (a) threaded holes (for example, holes 3047 ₁-3047 ₂) thatlocate connection mechanisms (for example and without limitation,releasable connection mechanisms) comprised, for example and withoutlimitation, of screws 3052 ₁-3052 ₂, which connection mechanisms areused to connect socket interposer 3050 and clamp 3060 (as will bedescribed below); and (b) holes (for example, holes 3049 ₁-3049 ₂) thatlocate connection mechanisms (for example and without limitation,releasable connection mechanisms) comprised, for example and withoutlimitation, of screws 3055 ₁-3055 ₂ and nuts 3057 ₁-3057 ₂, whichconnection mechanisms are used to connect Probe Card 3070 and socketinterposer 3050 (as will be described below). The thickness of socketinterposer 3050 is a function of the length of the Pogo pins. Socketinterposer 3050 may be fabricated in accordance with any one of a numberof methods that are well known to those of ordinary skill in the artsuch as, for example and without limitation, by injection molding, andthe holes may be fabricated therein in accordance with any one of anumber of methods that are well known to those of ordinary skill in theart such as, for example and without limitation, by drilling.

[0099] As further shown in FIG. 18, clamp 3060 includes: (a) for exampleand without limitation, four (4) holes (for example, holes 3061 ₁-3061₂) that locate connection mechanisms (for example and withoutlimitation, releasable connection mechanisms) comprised, for example andwithout limitation, of screws 3052 ₁-3052 ₂, which connection mechanismsare used to connect socket interposer 3050 and clamp 3060; (b) openregion 3080 having an area (in a plane perpendicular to the plane ofFIG. 18) that is larger than that of flex substrate 3010 and compliantadhesive layer 3040; (c) lip 3069 that fits over, and makes contact,when structure 3000 is assembled, with at least a portion of (andpreferably most of) a portion of substrate 3020 that extends beyondcompliant adhesive layer 3040 (for example and without limitation, atleast two or more edges); and (d) wing 3073 that provides a locationwherein clamp 3060 may be connected to socket interposer 3050.

[0100] In a second stage of the method for assembling structure 3000, ina first optional step, a release film such as, for example and withoutlimitation, a Mylar film or a Teflon film, is aligned with, and placedover, a base plate of the pinalignment fixture (as was described above,holes in the release film match the positions of alignment pins). Next,Probe Card 3070 is aligned with, and placed over, the release film onthe pinalignment fixture (holes in Probe Card 3070 (not shown) match thepositions of the alignment pins). Next, socket interposer 3050 isaligned with, and placed over, Probe Card 3070 on the pinalignmentfixture (holes in socket interposer 3050 (not shown) match the positionsof the alignment pins). Alignment pins are used on opposite corners andplaced through socket interposer 3050 and Probe Card 3070 to align theholes in socket interposer 3050 to the pads on Probe Card 3050. Next,socket interposer 3050 is connected to Probe Card 3070 using connectionmechanisms, for example, by inserting screws (for example, 3055 ₁-3055₂) through socket interposer 3050 and by affixing nuts (for example,nuts 3057 ₁-3057 ₂) to the screws. The alignment pins are then removed.Next, Pogo pins (for example, Pogo pins 3030 ₁-3030 ₂) are placed insidethe holes (for example, holes 3045 ₁-3045 ₂) in socket interposer 3050.Next, the intermediary structure formed during the first stage isaligned with, and placed over, socket interposer 3050 on thepinalignment fixture (holes in substrate 3020 of the intermediarystructure (not shown) match the positions of the alignment pins). Next,clamp 3060 is aligned with, and placed over, substrate 3020 and socketinterposer 3050 on the pinalignment fixture (holes in clamp 3060 (notshown) match the positions of the alignment pins). Next, clamp 3060 isattached to socket interposer 3050 using connection mechanisms (forexample, screws 3052 ₁-3052 ₂) to form structure 3000. The alignmentpins going through substrate 3010 and socket interposer 3050 are thenremoved. At this point, structure 3000 is removed from the pinalignmentstructure.

[0101] In accordance with one or more alternative embodiments of thepresent invention, compliant adhesive layer 3040 of structure 3000 isreplaced with a layer wherein an area directly under the post and bumps(for example, posts or bumps 3005 ₁-3005 ₂) on the top side of flexsubstrate 3010 is a compliant adhesive material that may be fabricatedusing any one of a number of materials that are well known to those ofordinary skill in the art such as, for example and without limitation, asilicon elastomer, a flexible epoxy, and so forth. Then, in accordancewith one or more such alternative embodiments of the present invention,the remainder of the layer may be a non-compliant adhesive such as, forexample and without limitation, polyimide having an adhesive (forexample and without limitation, epoxy, acrylic, epoxy-acrylic, and soforth) on both sides, and so forth. In accordance with one or morefurther alternative embodiment of the present invention, compliantadhesive layer 3040 of structure 3000 is replaced with a layer whereinan area directly under the post and bumps (for example, posts or bumps3005 ₁-3005 ₂) on the top side of flex substrate 3010 is open (i.e., airor even some other gas). Then, in accordance with one or more suchfurther alternative embodiments of the present invention, the remainderof the layer may be any of the compliant adhesives described above orany of the non-compliant adhesives described above.

[0102] In accordance with one or more still further alternativeembodiments of the present invention, substrate 3020 and socketinterposer 3050 of structure 3000 may be fabricated as a single layer.In accordance with one or more such still further alternativeembodiments, the above-described assembly procedure would be modified sothat the Pogo pins are inserted into the vias in compliant adhesivelayer 3040 before substrate 3020 is placed over compliant adhesive layer3040. In addition, in accordance with one or more still furtheralternative embodiments, clamp 3060 may be connected directly to ProbeCard 3070. In accordance with such one or more still further alternativeembodiments, socket interposer 3050 (or substrate 3020 if substrate 3020and socket interposer 3050 are fabricated as a single layer) may eitherbe connected separately to Probe Card 3070, or be held down by clamp3060.

[0103] One or more of the substrates described above have contactors onone side to contact I/O on an IC, for example, an IC on a wafer (bumpedor not), which contactors are formed of posts and/or bumps. However, itshould be understood that one or more of the above-described embodimentsinclude substrates wherein the contactors are formed of pads. Such padcontactors are useful, for example, for testing ICs on wafers havingbumped I/O.

[0104] Although various embodiments that incorporate the teachings ofthe present invention have been shown and described in detail herein,those skilled in the art can readily devise many other variedembodiments that still incorporate these teachings.

What is claimed is:
 1. A structure useful for testing circuits thatcomprises: a substrate having contactors on a first side and pads on asecond side; a card having pads on a first side; and interconnectorsthat electrically connect the pads on the second side of the substratewith the pads on the card; wherein at least one of the interconnectorsincludes at least a portion that does not melt at temperatures in arange from about 183° C. to about 230° C., and the distance between thesubstrate and the card is determined by a dimension of the at least aportion.
 2. The structure of claim 1 wherein the interconnectors aremetal balls.
 3. The structure of claim 2 wherein at least one of theinterconnectors is one of: a solid Cu ball, a solid Indium alloy ball,and a solid high lead solder ball.
 4. The structure of claim 1 whereinat least one of the interconnectors is a ceramic ball, wherein theceramic is embedded with a conducting material.
 5. The structure ofclaim 4 wherein the conducting material is one or more of: gold, Cu,silver, Ni, and an Indium alloy.
 6. A structure useful for testingcircuits that comprises: a substrate having contactors on a first sideand pads on a second side; a card having pads on a first side; andinterconnectors that electrically connect the pads on the second side ofthe substrate with the pads on the card; wherein at least one of theinterconnectors is a conductive, compliant ball.
 7. The structure ofclaim 6 wherein the conductive, compliant ball comprises a plastic corethat is surrounded by one or more layers of metal.
 8. The structure ofclaim 7 wherein the one or more layers of metal comprise one or more of:a layer of Cu; a layer of Ni; and a layer of Au.
 9. The structure ofclaim 7 wherein the plastic core is hollow.
 10. The structure of claim 8wherein the plastic core is hollow.
 11. A structure useful for testingcircuits that comprises: a substrate having contactors on a first sideand pads on a second side; a card having pads on a first side; andinterconnectors that electrically connect the pads on the second side ofthe substrate with pads on the card; wherein at least one of theinterconnectors is a spring.
 12. The structure of claim 1 wherein theinterconnectors are partially disposed in vias in an interconnectoralignment film.
 13. The structure of claim 1 wherein the dimension ofthe at least a portion is larger than a thickness of the interconnectoralignment film.
 14. The structure of claim 1 wherein the substrate oneof: a rigid substrate, a flex substrate, a semi-flex substrate, asilicon substrate, and a glass substrate.
 15. The structure of claim 1wherein the card is a Probe Card, and wherein the structure furthercomprises a stiffening mechanism affixed to a second side of the card.16. The structure of claim 15 wherein the stiffening mechanism comprisesa ring structure.
 17. The structure of claim 16 wherein the ringstructure comprises one or more of: radial arms, struts, and ribs. 18.The structure of claim 1 wherein: (a) the substrate is a flexiblesubstrate; (b) the contactors are disposed in an area on the first sideof the substrate; and (c) the pads on the substrate are disposed outsideof a projection of the area to the second side of the substrate.
 19. Astructure useful for testing circuits that comprises: a substrate havingcontactors on a first side and pads on a second side, wherein at leasttwo edges of the substrate have bevels; a card having pads on a firstside; interconnectors that electrically connect the pads on the secondside of the substrate with the pads on the card; and a clamp that isadapted to fit over the substrate, the clamp having an opening toprovide access to the contactors and a lip disposed over the bevels,which clamp is connected to the card; wherein at least one of theinterconnectors is compliant.
 20. The structure of claim 19 wherein thecompliant interconnector is a conductive, compliant ball.
 21. Thestructure of claim 19 wherein the compliant interconnector is a spring.22. The structure of claim 19 wherein the interconnectors are partiallydisposed in vias in an interconnector alignment film.
 23. The structureof claim 19 wherein the substrate is a silicon substrate.
 24. Thestructure of claim 7 wherein the plastic core is hollow.
 25. Thestructure of claim 8 wherein the plastic core is hollow.
 26. A structureuseful for testing circuits that comprises: a substrate havingcontactors on a first side and pads on a second side; a card having padson a first side; and interconnectors that electrically connect the padson the second side of the substrate with the pads on the card; whereinthe interconnectors include eutectic solder balls that are affixed tothe substrate and the card by cured conductive paste, and the distancebetween the substrate and the card is determined by a dimension of theeutectic solder balls.